The data communications industry has established the fiber distributed data interface (FDDI) as a standard for the definition of the properties of a local area network. A system in accordance with that standard is referred to as an FDDI system and is an optical system port to port operating at a data line rate of 125 megabits per second.
FDDI is the first, all optical fiber high speed local area network system and will become prominent in the last decade of the twentieth century. It will provide a high speed optical transmission path between mainframe and peripheral equipment and is suitable for use as a backbone network between lower speed local area networks. FDDI presently is a 100 megabit LAN transfer rate system that recommends a 62.5/125 micron core/cladding diameter optical fiber and is an LED based standard involving dual, counter-rotating, token passing rings that operate at a center wavelength of 1300 nm.
Dual rings include a primary ring and a secondary ring. Dual rings are used to provide enhanced reliability and an option for higher performance. If both rings are operative, the capability of transmitting in both ring directions exists.
The large scale use of optical fiber for the local area network will result in an extensive use of optical fiber in building distribution systems. The FDDI system presents several challenges. There are restrictions imposed by FDDI standards and there are complications associated with large quantities of fiber that include fiber which extends to individual work stations. In order to aid network engineers and installers in enforcing basic rules and/or more restrictive policies which may be chosen by the user, the FDDI standard has defined certain requirements.
Details of a receptacle for a dual fiber connector are specified in a standard referred to as the Physical Layer Medium Dependent (PMD) part of the FDDI standard. The PMD determines the specifications for optical transmitters and receivers, optical fiber, optical connections and optical bypass switches along with optional keying configurations. The receptacle and an associated plug are polarized mechanically to prevent the transposition of transmit/receive fibers, and keys corresponding to station interfaces are designed to avoid mixing primary and secondary rings and to avoid mixing station attachments. Viewing a station with the key on top, the transmit signal always exits the interface on a left fiber port, and the receive signal always enters the interface on a right fiber port.
A simple dual ring architecture can be arranged with the keying and signal directions defined in the PMD standard by using duplex jumper cables. The primary ring is constructed by connecting a B receptacle of each station to an A receptacle of the next station in a forward direction around the primary ring. When the primary ring is closed, the secondary ring is completed with the secondary ring signal flowing in an opposite direction.
Networks may be as simple as one which includes a station interconnecting within a common data center connected to an equipment room, as common as one which includes stations which connect within a single multi-floor building or as complicated as one which interconnects a campus involving several buildings. As long as the rings are confined to a relatively small area such as a data center, for example, a simple fiber topology which includes duplex jumpers that interconnect the network nodes is relatively easy to install and administer.
The prior art includes such a simple fiber topology for a single floor on which are disposed a plurality of stations. For a dual ring, counter rotating topology, each station includes two sets of ports each set associated with a receptacle. One port of one set (B receptacle) is an output port for the primary ring and the other port, an input port for the secondary ring. The other set of ports (A receptacle) for each station includes an output port for the secondary ring and an input port for the primary ring. Jumpers connect the primary output port of each station to the primary input port of a next successive station until a primary ring has been completed through all the stations. Likewise, the secondary ring is completed by connecting the secondary output port of each station in an opposite ring direction to the secondary input port of an adjacent station.
As the network expands to multiple floors of a single building or to a campus including multiple buildings, connections become prohibitively complex to administer. For such expanded networks, it should be clear that a manageable distribution system is necessary. Desirably, the sought-after system should be one which includes simplistic rules for installation and administration.
What is needed is a strategy for implementing a network in a mechanistic way without having to understand the architecture. Without the sought-after system, a craftsperson would have to trace an optical signal through the network for every fiber path which is prohibitively difficult and time consuming. Also, without such a system, repairs would require higher skill levels.